On Thu, Jan 27, 2022 at 2:05 PM Hans de Goede hdegoede@redhat.com wrote:
Hi,
On 1/26/22 18:11, Rafael J. Wysocki wrote:
On Wed, Jan 26, 2022 at 5:41 PM Hans de Goede hdegoede@redhat.com wrote:
Hi,
On 1/26/22 16:54, Rafael J. Wysocki wrote:
On Wed, Jan 26, 2022 at 2:47 PM Hans de Goede hdegoede@redhat.com wrote:
Hi All,
On 1/23/22 10:10, Tong Zhang wrote:
when acpi=off is provided in bootarg, kernel crash with
[ 1.252739] BUG: kernel NULL pointer dereference, address: 0000000000000018 [ 1.258308] Call Trace: [ 1.258490] ? acpi_walk_namespace+0x147/0x147 [ 1.258770] acpi_get_devices+0xe4/0x137 [ 1.258921] ? drm_core_init+0xc0/0xc0 [drm] [ 1.259108] detect_thinkpad_privacy_screen+0x5e/0xa8 [drm] [ 1.259337] drm_privacy_screen_lookup_init+0xe/0xe85 [drm]
The reason is that acpi_walk_namespace expects acpi related stuff initialized but in fact it wouldn't when acpi is set to off. In this case we should honor acpi=off in detect_thinkpad_privacy_screen().
Signed-off-by: Tong Zhang ztong0001@gmail.com
Thank you for catching this and thank you for your patch. I was about to merge this, but then I realized that this might not be the best way to fix this.
A quick grep shows 10 acpi_get_devices() calls outside of drivers/acpi, and at a first glance about half of those are missing an acpi_disabled check. IMHO it would be better to simply add an acpi_disabled check to acpi_get_devices() itself.
Rafael, do you agree ?
Yes, I do.
Did you see my follow-up that that is not going to work because acpi_get_devices() is an acpica function ?
No, I didn't, but it is possible to add a wrapper doing the check around it and convert all of the users.
Yes I did think about that. Note that I've gone ahead and pushed the fix which started this to drm-misc-fixes, to resolve the crash for now.
OK
If we add such a wrapper we can remove a bunch of acpi_disabled checks from various callers.
Alternatively, the ACPICA function can check acpi_gbl_root_node against NULL, like in the attached (untested) patch.
That is probably an even better idea, as that avoids the need for a wrapper altogether. So I believe that that is the best solution.
Allright, let me cut an analogous patch for the upstream ACPICA, then.